1. Field of the Invention
This invention relates to a process for removal of spinning solvents from solution spun fibers. More particularly, this invention relates to a process for extraction of a spinning solvent from solution spun fiber in which the solution is spun into a coagulation or gelation liquid.
2. Prior Art
The preparation of fibers through gel spinning and solution spinning process are known. For example, U.S. Pat. Nos. 4,413,110, 4,455,273, 4,536,536, 4,551,296 describes a process in polyolefin fibers having a molecular weight equal to or greater than 500,000. In these processes, a hot dilute solution (2-30%) of a polyolefin in a relatively non-volatile solvent such as an aliphatic or aromatic hydrocarbon as for example mineral oil, paraffin oil, decalin, poly(ethylene) wax or mixtures thereof is spun. The spun hot solution is cooled forming a gel or coagulate fiber. The resultant gel or coagulate fiber is extracted with another solvent which extracts the spinning solvent and replaces it in the fiber, and is then dried. The fiber is stretched at one or more stages during the process to provide a dried fiber having the desired tenacity and modulus.
Kalb and Penning in Polymer Bulletin, vol. 1, pp. 87914 80 (1979), Polymer, 2584-90 (1980) and Smook et al. in Polymer Bull., vol. 2, pp. 775-83 (1980) describe a process in which the polyethylene is dissolved in a non-volatile solvent (paraffin oil) and the solution is cooled to room temperature to form a gel. The gel is cut into pieces, fed to an extruder and spun into a gel filament. The gel filament is extracted with hexane to remove the paraffin oil, vacuum dried and then stretched to form the desired fiber.
U.S. Pat. Nos. 4,440,711, 4,713,290, and 4,883,628 describe processes for the gel spinning fibers formed from polymers formed from vinyl alcohol and acrylonitrile. Polymer of a molecular weight of over 500,000 is spun as a dilute solution (2-15%) in a relatively non-volatile solvent such as glycerin, dimethylsulfoxide, dimethylformamide, and ethylene carbonate. The resultant solvent is extracted with a volatile solvent such as methanol and water, the extracted fiber is dried. Upon stretching at one or more stages during the process, fibers of tenacity above 5 g/denier and modulus above 100 g/denier are produced.
Zwick et al. in Soc Chem Ind, London, Monograph No. 30, pp. 188-207 (1968) describe the spinning of poly(vinyl alcohol) by a Phase Separation technique said to differ from earlier Wet Spinning, Dry Spinning and Gel Spinning techniques. The reference indicates that the earlier systems employ 10-20% , 25-40% and 45-55% polymer concentrations, respectively, and that they differ in the manner in which low molecular weight materials (solvents such as water) are removed. The reference also indicates some earlier systems to be restricted in spinneret hole size, attenuation permitted or required, maximum production speed and attainable fiber properties.
The Phase Separation process described in Zwick et al. (see also UK Patent Specification 1,100,497) employs a polymer content of 10-25% (broadly 5-25% in the Patent which covers other polymers as well) dissolved at high temperatures in a one or two-component solvent (low molecular weight component) system that phase separates on cooling. This phase separation took the form of polymer gelation and solidification of the solvent (or one of its components), although the latter is indicated in the Patent to be optional. The solution was extruded through apertures at the high temperature through unheated air and wound up at high speeds hundreds or thousands of times greater than the linear velocity of the polymer solution through the aperture. Thereafter the fibers were extracted to remove the included or exterior solvent phase, dried and stretched. An earlier, more general description of Phase Separation Spinning is contained in Zwick Applied Polymer Symposia, no. 6, pp. 109-49 (1967).
Modifications in the spinning of hot solutions of ultrahigh molecular weight poly(ethylene) (see Examples 21-23 of UK 1,100,497) have been reported by Smith and Lemstra and by Pennings and coworkers in various articles and patents including German Offen 3004699 (Aug. 21, 1980); UK Application 2,051,667 (Jan. 21, 1981); Polymer Bulletin, vol. 1, pp. 879-880 (1979) and vol. 2, pp. 775-83 (1980); and Polymer 2584-909 1980).
The Zwick et al article states the poly(vinyl alcohol) content of 10-25% in the polymer solution to be optimal, at least in the system explored in most detail where the solvent or a component of the solvent solidified on the cooling to concentrate the poly(vinyl alcohol) in the liquid phase on cooling before the poly(vinyl alcohol) gels. Unlike the systems used in the Kavesh et al applications and Smith and Lemstra patents, all three versions of Zwick's Phase Separation process take up the fiber directly from the air gap, without a quench bath, such that the draw-down occurred over a relatively large length of cooling fibers.
U.S. Pat. No. 4,771,616 relates to an apparatus and method for extraction of a material from a running length of fiber. This method comprises continuously moving the fiber through a conduit while simultaneously flowing a solvent for the material through the conduit with the conduit having a length and cross sectional area sufficient to facilitate extraction of the desired amount of the material. The flow is preferred to be countercurrent to the movement of the fiber.
A prior method to extract mineral oil from polyethylene solution spun fiber and a method to manufacture such fiber is disclosed in U.S. Pat. No. 4,413,110 hereby incorporated by reference. A process to purify both the solvent and the mineral oil for recycle and/or reuse is disclosed in pending U.S. Ser. No. 811,123 filed Dec. 19, 1985, hereby incorporated by reference. A prior art method for treatment of filamentary materials in a tube is found in U.S. Pat. No. 2,509,279.
U.S. Pat. No. 4,334,102 describes a method for removing liquid hydrocarbons from polyether solvents such as dimethyl ether of polyethylene glycol. The method comprises the steps of mixing the solution with an aqueous salt solution, removing at a low temperature an organic layer containing liquid hydrocarbons, heating the remaining aqueous layer to a higher temperature where it separates into a second organic layer containing polyether solvent and an aqueous salt solution. The aqueous salt solution is cooled and recycled to mix with additional polyether solvent solution at the low temperature. The process is particularly applicable to removing liquid hydrocarbons which accumulate in recirculating polyether solvents used for absorption of acid gases from feedstocks such as natural gas, synthetic natural gas, ammonia synthesis gas and refinery gas.